Pubic symphysis

The pubic symphysis (or symphysis pubis) is a midline secondary amphiarthrodial cartilaginous joint of the bony pelvis, uniting both pubic bodies.

Gross anatomy

Articulations

The pubic symphysis is a secondary cartilaginous joint, which means there is a wedge-shaped fibrocartilaginous interpubic disc situated between two layers of hyaline cartilage, which line the oval-shaped medial articular surfaces of the pubic bones ^1-2. 

The width of the joint space differs at different ages:

• ~10 mm at 3 years
• ~6 mm at 20 years
• ~3 mm at 50 years

For physiological reasons, women have a greater thickness of the fibrocartilaginous disc, allowing more mobility of the pelvic bones and thereby providing a larger pelvic diameter needed for childbirth.

Attachments

Ligaments

The pubic symphysis is reinforced by four strong ligaments ^2-3:

• superior pubic ligament: runs from pubic crest to pubic crest
• inferior pubic (or subpubic or arcuate) ligament: runs from inferior pubic ramus to inferior pubic ramus
• anterior pubic ligament: blends with periosteum laterally as well as the interpubic disc
• posterior pubic ligament: blends with periosteum of both pubic bodies posteriorly

Other ligaments which attach to the pubic symphysis include:

• suspensory ligament of the penis
• pubocervical ligament

Musculotendinous

• adductor longus, adductor brevis and rectus abdominis muscles attach to the anterior pubic ligament and interpubic disc ²
• external oblique aponeurosis also reinforces the pubic symphysis anteriorly ³
• remaining anterior abdominal wall muscles (internal oblique, tranversus abdominis) ⁷
• remaining thigh adductor muscles (adductor magnus, pectineus, gracilis) ⁷
• pyramidalis muscle

Relations

• anteriorly
  • proximal ends of the penile/clitoral shafts
• inferiorly
  • urethra
  • deep dorsal vein of penis/clitoris
• posteriorly
  • bladder (separated from the pubic symphysis by the retropubic fat pad)
  • prostate and prostatic venous plexus

Movement

Normally very little movement: up to 2 mm shift and 1° rotation ².

Blood supply

• mainly supplied by branches of obturator and inferior epigastric arteries ²

Innervation

• supplied by branches of the pudendal and/or genitofemoral and/or iliohypogastric/ilioinguinal nerves ²

Variant anatomy

• congenital widening of the pubic symphysis (rare) ⁵

Radiographic features

CT/MRI

• due to anteriorly-situated secondary ossification centers may appear "V-shaped" in adolescents on axial slices but will normally be parallel in adults ¹

Related pathology

• parturition-induced pelvic instability
• pubic symphysis widening (mnemonic)
• open book fracture of the pelvis
• osteitis pubis
• pubic symphysis fusion (or bridging)